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Abstract：
Brassinosteroids (BRs) are steroid hormones that modulate numerous physiological processes in plants. However, few studies have focused on the involvement of BRs in sensing and responding to the stress of mineral nutrient deficiency. In the present study, we evaluated the roles of BRs in the response of rice (Oryza sativa) to iron (Fe) deficiency during Fe uptake, transport, and translocation. Exogenous application of 24-epibrassinolide (EBR) to wild-type (WT) plants exaggerated leaf symptoms of Fe deficiency and suppressed growth. EBR increased and decreased Fe concentrations in roots and shoots, respectively, under both Fe-deficient and Fe-sufficient conditions. Transcripts involved in Fe homeostasis, including OsIRT1, OsYSL15, OsYSL2, OsNAS1, and OsNAS2, were enhanced by EBR under Fe-deficient conditions. EBR depressed expression of OsNAS1, OsNAS2, and OsYSL2 in shoots, and inhibited Fe transport and translocation via the phloem. Rice mutant d2-1, which is defective in BR biosynthesis, was more tolerant to Fe deficiency than the WT, and accumulated greater amounts of Fe in roots than the WT under Fe-sufficient conditions. A greater upregulation of OsIRT1, OsYSL15, OsYSL2, OsNAS1, and OsNAS2 in the d2-1 mutant compared to the WT was found under Fe-sufficient conditions, while expression of these genes in the d2-1 mutant was lower than in the WT under Fe-deficient conditions. The greater tolerance of the d2-1 mutant could be partly mitigated by exogenous application of EBR. These novel findings highlight the important role of BR in mediating the response of strategy II plants to Fe deficiency by regulating Fe uptake and translocation in rice.
摘要：
油菜素类固醇(BRs)是调节植物中许多生理过程的类固醇激素。然而,很少有研究关注BRs在感知和响应矿物质营养缺乏应激中的作用。在本研究中,我们评估了BRs在水稻（Oryzasativa）对铁吸收过程中铁（Fe）缺乏的反应中的作用，运输,和易位。24-表油菜素内酯（EBR）对野生型（WT）植物的外源应用夸大了缺铁的叶片症状并抑制了生长。EBR增加和减少根和芽中的铁浓度，分别,在缺铁和铁充分条件下。涉及铁稳态的转录本，包括OsIRT1，OsYSL15，OsYSL2，OsNAS1和OsNAS2，在缺铁条件下通过EBR增强。EBR抑制了芽中OsNAS1，OsNAS2和OsYSL2的表达，并抑制Fe通过韧皮部的转运和转运。水稻突变体d2-1，在BR生物合成中存在缺陷，比WT更耐受铁缺乏症，在铁充足的条件下，根中积累的铁含量比WT高。在Fe充足的条件下，与WT相比，d2-1突变体中OsIRT1，OsYSL15，OsYSL2，OsNAS1和OsNAS2的上调更大。而在Fe缺乏条件下，d2-1突变体中这些基因的表达低于WT。d2-1突变体的更大耐受性可以通过外源应用EBR部分减轻。这些新发现强调了BR通过调节水稻中的Fe吸收和转运在介导策略II植物对Fe缺乏的反应中的重要作用。
